It was a completely flat roof until a few years ago, when they did away with the roof rock and went the route of shingles. The roofers added a very slight angle, enough to keep water from collecting, but it is still very flat. On the inside, there are only rafters and plywood. We cut a hole in one corner of the roof. They have two water heaters, one gas(garage corner), one solar (outside). We cut a hole in the roof between two rafters, basically above the heater and the fan exhausts straight up into a galvanized t-top roof vent.
Similar to this one:
The fan runs for about 10 hours a day, 365 days a year. I have yet to replace the brushes in the motor.